System and method for reducing dropped calls in a wireless communications network

ABSTRACT

A system and method for managing wireless communications system resources. The system includes a first mechanism that determines currently available wireless communications system traffic resources and provides a signal in response thereto. A second mechanism de-allocates wireless communications system supplemental resources and reallocates the supplemental resources as traffic resources in response to the signal. In a specific embodiment, the currently available wireless communications system traffic resources include currently available traffic channels, and the supplemental resources include supplemental channels. The first mechanism includes a mechanism that compares a number of in-use traffic channels with a number of total traffic channels and provides the signal when the difference between the number of total traffic channels and the number of in-use traffic channels is less than a predetermined threshold. The first mechanism further includes a mechanism that monitors when a call handoff request and/or a call origination request is blocked at a base station transceiver subsystem call resource manager and provides the signal when the call is blocked. The second mechanism includes a mechanism for sending a message to a selector bank subsystem radio link manager, receiving a response from the selector bank subsystem radio link manager and de-allocating the supplemental resources.

BACKGROUND OF THE INVENTION

I. Field of Invention

This invention relates to wireless communications systems. Specifically,the present invention relates systems and methods for allocating trafficchannels and supplemental channels in a base station or base stationtransceiver subsystem (BTS).

II. Description of the Related Art

Cellular telecommunications systems are characterized by a plurality ofmobile stations (e.g. cellular telephones, mobile units, wirelesstelephones, or mobile phones) in communication with one or more basestation transceiver subsystems (BTSs). Signals transmitted by the mobilestations are received by a BTS and often relayed to a mobile switchingcenter (MSC) having a base station controller (BSC). The MSC, in turn,routes the signal to a public switched telephone network (PSTN) or toanother mobile station. Similarly, a signal may be transmitted from thepublic switched telephone network to a mobile station via a base stationor BTS and an MSC.

Each BTS covers a ‘cell’ within which a mobile station may communicate.A cell covers a limited geographic area and routes calls from mobilestations to and from a telecommunications network via an MSC. Thecoverage area of a typical cellular telecommunications system is dividedinto several cells. Different communications resources such asfrequencies are often allocated to each cell to maximize communicationssystem resources. When a mobile station moves from a first cell to asecond cell, a handoff is performed to assign new system resourcesassociated with the second cell.

A handoff involves the execution of a set of negotiation instructionsbetween the mobile station and one or more governing BTSs and/or MSCs.Cellular telecommunications systems generally require efficient andreliable handoff procedures to maximize the utilization of systemresources. Efficient and reliable handoff procedures are becomingincreasingly important as smaller cells are deployed to meet demands forincreased communications system capacity. Use of the smaller cellsincreases the number of cell boundary crossings and frequencyassignments thereby increasing the need for efficient and cost-effectivehandoff mechanisms and procedures.

To facilitate handoff between adjacent cells, a handoff beacon is oftenemployed. A beacon in each cell broadcasts a signal having a limitedrange about the cell. When a mobile station in a first cell detects abeacon from a second cell, the telephone is handed off to the secondcell.

A BTS routes calls between mobile stations within a predeterminedgeographic area, i.e., cell governed by the BTS, and to and from an MSCand a BSC. The MSC and BSC facilitate the routing of calls between BTSsand between the wireless communications network and the PSTN, i.e.,wireline network.

A BSC or MSC is often associated with a particular geographic areacomprising one or more cells and often includes various components suchas a selector bank subsystem (SBS) and radio link manager (RLM) tofacilitate the allocation of network resources between voice calls andother network functions. Network resources may include computer memory,bandwidth, and other hardware and software.

Typically some network resources are assigned to traffic channels andsome network resources are assigned to supplemental channels. The use oftraffic channels and supplementary channels in wirelesstelecommunications networks is discussed in IS-95 telecommunicationsindustry standard documentation.

Supplemental channels often carry data such as a file transferredbetween two wireless computer modems. Fundamental traffic channels oftencarry voice calls and/or data calls over the wireless network. Toimprove the quality of a given voice and/or data call, additionalsupplemental channels may be added to the traffic channel associatedwith the voice and/or data. The additional supplemental channelsincrease the throughput of the wireless link between the mobile stationand the base station.

When a mobile station, maintaining a call, travels from a first systemcoverage area associated with a first BSC (or BTS) to a second systemcoverage area associated with a second BSC (or BTS), the mobile stationis handed off to the second BSC (or BTS) and associated BTS(s). If thetarget BTS associated with the second BSC (or BTS) has insufficienttraffic channels to accommodate the handoff, the handoff is typicallyblocked by a call resource manager (CRM) of the target BTS, and the callis dropped. Hence, when all traffic channels in a BTS are in use, anyadditional calls handed off to the BTS are typically dropped, and anynewly originated calls are typically blocked.

Hence, a need exists in the art for an efficient and cost effectivesystem for reducing dropped or blocked calls due to insufficient trafficchannel resources. There exists a further need for an efficient methodfor allocating and de-allocating traffic channels and supplementarychannels.

SUMMARY OF THE INVENTION

The need in the art is addressed by the system for managing wirelesscommunications system resources of the present invention. In theillustrative embodiment, the present invention is implemented insoftware running on a computer within a base station in a wirelesscommunications system and includes a first mechanism for determiningcurrently available wireless communications system traffic resources andproviding a signal in response thereto. A second mechanism de-allocateswireless communications system supplemental resources and reallocatesthe supplemental resources as traffic resources in response to thesignal.

In a specific embodiment, the currently available wirelesscommunications system traffic resources include currently availabletraffic channels, and the supplemental resources include supplementalchannels. The first mechanism includes code for comparing a number ofin-use traffic channels with a number of total traffic channels andproviding the signal when the difference between the number of totaltraffic channels and the number of in-use traffic channels is less thana predetermined threshold.

The first mechanism further includes code for monitoring when a callhandoff request is blocked at a base station call resource manager andproviding the signal when the call is blocked. The second mechanismincludes code for sending a message to a selector bank subsystem radiolink manager, receiving a response from the selector bank subsystemradio link manager, de-allocating the supplemental resources, andreallocating the supplemental resources as traffic resources.

In the illustrative embodiment, the invention is implemented in softwarerunning on a computer within the wireless communications network thatstrategically controls, via the first and second mechanisms, theallocation of supplemental channels in response to changing networktraffic. By strategically controlling the allocation of supplementalchannels, the present invention reduces dropped or blocked calls duringhandoffs, reduces blocked or dropped calls during call origination, andincreases the overall reliability of the associated wirelesscommunications system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary code division multiple access(CDMA) cellular telephone system for which the present invention isadapted.

FIG. 2 is a more detailed diagram showing the mobile switching center(MSC), the base station controller (BSC), the first base stationtransceiver subsystem (BTS), and the mobile station of FIG. 1.

FIG. 3 is a ping-pong diagram illustrating messages exchanged betweenthe RLM, CRM, and the TCE of FIG. 2 to set up a call in accordance withthe to teachings of the present invention.

FIG. 4 is a ping-pong diagram illustrating messages exchanged betweenthe radio link manager (RLM), the call resource manager (CRM), and thetraffic channel element (TCE) of FIG. 2 to facilitate mobile stationmobility according to the present invention.

FIG. 5 is a flow diagram of a method for strategically allocatingsupplemental channels to reduce dropped calls during handoff ororigination implemented within the BTS and BSC of FIG. 2.

FIG. 6 is a flow diagram of a method for allocating supplementalchannels and traffic channels according to the present invention.

DESCRIPTION OF THE INVENTION

While the present invention is described herein with reference toillustrative embodiments for particular applications, it should beunderstood that the invention is not limited thereto. Those havingordinary skill in the art and access to the teachings provided hereinwill recognize additional modifications, applications, and embodimentswithin the scope thereof and additional fields in which the presentinvention would be of significant utility.

FIG. 1 is a block diagram of an exemplary cellular telephone system 10for which the present invention is adapted. The system 10 includes amobile switching center (MSC) 12 having a base station controller (BSC)14. A public switched telephone network (PSTN) 16 routes calls fromtelephone lines and other networks (not shown) to and from the MSC 12.The MSC 12 routes calls from the PSTN 16 to and from a first BTS 18 anda second BTS 20 associated with a first cell 22 and a second cell 24,respectively. The BTSs 18 and 20 are often called cell controllers.

The MSC 12 routes calls between the BTSs 18 and 20. The first BTS 18directs calls to the first mobile station 26 within the first cell 22via a first communications link 28. The communications link 28 is atwo-way link having a forward link 30 and a reverse link 32. Typically,when the BTS 18 has established voice communications with the mobilestation 26, the link 28 is characterized as a traffic channel. Althougheach BTS 18 and 20 is associated with only one cell, a BSC is oftengoverns or is associated with several cells.

When the mobile station 26 moves from the first cell 22 to the secondcell 24, the mobile station 26 is handed off to the second BTS 20.Handoff typically occurs in an overlap region 36 where the first cell 22overlaps the second cell 24.

In a soft handoff, the mobile station 26 establishes a secondcommunications link 34 with the target BTS 20 in addition to the firstcommunications link 28 with the source BTS 18. During a soft handoff,both the first link 28 and the second link 34 are maintainedsimultaneously. After the mobile station 26 has crossed into the secondcell 24, it may drop the first communications link 28.

In a hard handoff, the communications link 34 is not established. Whenthe mobile station 26 moves from the first cell 22 to the second cell24, the link 28 to the source BTS 18 is dropped and a new link is formedwith the target BTS 20.

The present invention accommodates several types of call origination andhandoff including intersystem handoff and intrasystem handoff. Anintersystem handoff occurs when a mobile station operating under thecontrol of a given cellular telecommunications system, such as thesystem 10, moves outside the coverage area of the telecommunicationssystem and is handed off to an adjacent system (not shown). Intersystemhandoff is used when two telecommunication systems are adjacent to oneanother and the neighboring system is better able to serve the mobilestation 26 than the current serving system 10. The neighboring systemand the serving system 10 must have contiguous serving areas.Intersystem handoff can take place between two systems using the sameair interface or between two systems using two different air interfaces.

Intrasystem handoff occurs when a mobile station moves from one call(BTS) coverage area to another cell coverage area. Intrasystem handoffis often employed in systems having multiple frequencies assigned tosome BTSs to efficiently utilize spectrum resources and increase thecapacity of the CDMA network. Using multiple frequencies often providesadvantages over other methods aimed at capacity increase such as cellsplitting or cell sectorization. Intrasystem handoff can also happenbetween two networks of the same system using two different airinterfaces.

In multiple frequency systems, handoff is required when a mobile ismoving from an area that has multiple frequencies to an area that hasfewer frequencies. Handoff is also required when a mobile station ismoving from an area with small load on the serving frequency to an areawith high load on the serving frequency and load balancing is required.

FIG. 2 is a more detailed diagram showing the mobile switching center(MSC) 12, the base station controller (BSC) 14, the first base station(BTS) 18, and the mobile station 26 of FIG. 1. In FIG. 2 the system 10includes, from left to right, the mobile station 26, the base station18, the mobile switching center 12 having the base station controller 14and a supplementary services adjunct (SSA) 40, and the public switchedtelephone network (PSTN) 16.

The base station 18 has an overhead channel manager (OCM) 42, a callresource manager (CRM) 44, a BTS computer 46 (also known as a BTSC) thatincludes the OCM 42 and the CRM 44, and a traffic channel element (TCE)48. The BTS computer 46 controls the OCM 42 and the CRM 44 via software.The MSC 12 includes the BSC 14 and the SSA 40. The SSA 40 may bereplaced with a standard mobile switch without departing from the scopeof the present invention.

The BSC 14 includes a call control processor (CCP) 50, a time andfrequency unit (TFU) 52, and a selector bank subsystem (SBS) 54. The CCP50 includes a paging and access manager (PAM) 56. The SBS 54 includes aradio link manager (RLM) 58 and a traffic processing unit (TPU) 60. TheSSA 40 communicates with the CCP 50, the SBS 54, and the PSTN 16 andacts as a switch to facilitate the routing of calls between the MSC 12and the PSTN 16.

For clarity, the second base station 20 of FIG. 1 is omitted from FIG.2. In addition, various other system components are omitted; however,those skilled in the art will know where to obtain these components andhow they fit within the system 10. For example, components include acell site modem in the base station 18 for establishing theair-interface link 28 between the base station 18 and the mobile station26 and a code division multiple access (CDMA) interconnect subsystem forrouting messages from various elements within the base station 18 tovarious elements within the BSC 14 are omitted.

The OCM 42 in the base station 18 communicates with the PAM 56 and theTFU 52 in the BSC 14. A signaling link between the OCM 42 and the PAM 56is used for messages, such as mobile station origination messages andmessages pertaining to access and registration overload, which arereceived over an access channel. Messages directed to the mobile station26 travel from the PAM 56 to the OCM 42, and messages received from themobile station 26 flow from the OCM 42 to the PAM 56, which isimplemented within a selector card interface (not shown). A signalinglink between the OCM 42 and the TFU 52 is used for keep-alive messagessent by the TFU 52 to the OCM 42 to indicate a live backhaul connection.

The OCM 42 and the CRM 44 in the BTS 18 are controlled and/orimplemented via software running on the BTS computer 46. The BTScomputer 46, which includes a microprocessor (not shown), communicateswith the RLM 58, which is in the SBS 54 of the BSC 14. The BTS computer46 also communicates with the RLM 58 and runs unique softwareconstructed in accordance with the teachings of the present inventionand, as discussed more fully below, to manage traffic and supplementaryresources within the BTS 18.

A signaling link between the CRM 44 and the RLM 58 transfers networkoperation interface specification (NOIS) messages between the CRM 44 andthe RLM 58. NOIS messages are sent from the RLM 58 to the CRM 44 tofacilitate call resource allocation and call resource de-allocation.Response messages are sent from the CRM 44 to the RLM 58.

The TCE 48 in the BTS 18 communicates with the RLM 58 and the TPU 60 inthe SBS 54 of the BSC 14. A signaling link between the TCE 48 and theRLM 58 transfers NOIS messages between the TCE 48 and the RLM 58 tosupport traffic resource control operations. A traffic link between theTCE 48 and the TPU 60 transfers traffic messages between the TCE 48 andthe TPU 60. The message payload carries reverse link traffic channelframes from the TCE 48 to the TPU 60 and forward link traffic channelframes from the TPU 60 to the TCE 48. Frame quality and power controlinformation is also appended to the messages. The messages areconstructed in accordance with the IS-95A standard.

The computer 46 runs software to selectively allocate and de-allocatetraffic channels and supplementary channels based on total trafficresources, supplementary resources, and total currently availableresources. For example, the computer 46 monitors allocation of channelswithin the TCE 48 via the CRM 44 and the RLM 58 and maintains a trafficchannel threshold and a supplementary channel threshold. If the numberof remaining traffic channels not currently in use drops below thetraffic channel threshold, in-use supplementary channels arede-allocated and reallocated as traffic channels via a series ofmessages transferred between the CRM 44, the RLM 58, and the TCE 48 (asdiscussed more fully below). Supplementary channels are de-allocateduntil the number of available traffic channels exceeds the trafficchannel threshold. Also, the supplemental channels that are notcurrently in use may be used as traffic channels.

If the number of remaining traffic channels becomes less than thesupplementary channel threshold, supplementary channels will cease beingallocated and instead will be reserved for traffic channel use. Theactual values for the traffic channel threshold and the supplementarychannel threshold are application-dependent, and those having ordinaryskill in the art will easily be able to choose appropriate values tomeet the needs for a given application.

Alternatively, supplementary resources may be de-allocated at the lastminute to avoid a dropped call during a handoff procedure. For examplewhen a handoff request for a call is blocked at the CRM 44, the uniquesoftware running on the computer 46 may check the number of supplementalchannels currently in use at the TCE 48 via the RLM 58 or CRM 44. If thecall was blocked at the CRM 44 due to insufficient traffic channelresources, the software initiates a resource release request to be sentfrom the CRM 44 to the RLM 58 requesting that the RLM 58 releasesupplementary channel resources at the TCE 48.

In the present specific embodiment, before implementing the above steps,the software running on the computer 46 estimates a time required for aresource release request to be sent from the CRM 44 to the RLM 58, aresponse to be sent back to the CRM 44 for the supplementary channels tobe de-allocated at the TCE 48 and reallocated as traffic channels at theTCE 48 for an appropriate number of supplementary channels. If the timerequired is likely to cause a dropped call due to a timing problem, themethod is aborted.

The present invention is adapted for use with medium data rate (MDR)features. The medium data rate (MDR) IS-95 standard and associatedfeatures aims to increase data throughput without changinginfrastructure hardware. This is achieved by permitting a singlesubscriber to use up to 8 code channels on the forward link 30 and up to8 code channels on the reverse link 32. Additional code channels, termedsupplemental channels or supplementary channels, may be assigned to adata mobile station such as a computer modem.

A supplemental code channel is either transmitted at full rate (9600 bpsfor Rate Set 1 or 14400 bps for Rate Set 2) or not transmitted at all.It must use the same rate set as the fundamental code channel. It maycarry primary traffic or secondary traffic, but not both (i.e., nodim-and-burst). No signaling traffic is sent on the supplemental codechannel. When neither primary nor secondary traffic is available, thebase station 18 shall not transmit the forward supplemental codechannels. In addition, supplemental code channels do not have a reverselink power control sub-channel (no code puncturing), which gives someperformance improvement. Supplemental code channels have the same frameoffset as the associated fundamental channel.

A fundamental code channel is put in soft handoff using methods known inthe art and used for voice calls. Whenever the fundamental code channelis put in soft handoff, the associated supplemental code channels arealso put in soft handoff. Supplemental code channel symmetry must beachieved between the base stations. If there are not enough resourcesfor all the supplemental code channels on the new base station or BSC,some channels will be released by the requestor base station or BSC.

A forward link allows up to eight code channels to be combined togetherto provide up to eight times the current maximum data rate. These codechannels are the forward traffic channels defined in the IS-95A standardand are discriminated by Walsh codes assigned by the base station 18.The forward traffic channels are divided into two types: the fundamentalcode Channel and the associated supplement code channels.

A fundamental code channel is assigned to the mobile station 26 for adata call. A fundamental code channel is a standard forward trafficchannel that is transmitted at variable data rate. The fundamental codechannel may carry primary traffic, secondary traffic, or signalingtraffic. The fundamental code channel also has a reverse link powercontrol sub-channel as defined in IS-95A.

In the preferred embodiment, the CRM 44 has a threshold of remainingTCEs established via the computer 46, below which it will request theSBS 54 to de-allocate supplemental channels. For example, if the basestation 18 has a total of 60 TCEs (not shown) and the de-allocationrequest threshold is 55 TCEs, when the number of remaining TCEs reachesbelow 5 (60−55), the CRM 44 will send a request to the RLM 58corresponding to its first supplemental channel for a resource release(as discussed more fully below). Thus, for example, a 60 TCE systemcould have 20 supplementals allocated first, followed by 35 fundamentsand supplementals. When the number of remaining TCEs reach 5, the CRM 44starts requesting de-allocation of the supplementals.

The de-allocation request threshold does not necessarily correspond tothe supplemental blocking threshold for the TCEs. If for example, theCRM 44 has a supplemental blocking threshold that is x, and ade-allocation request threshold as y (y>x), the allocation ofsupplemental channels will be blocked after x TCEs are in use. Anattempt to de-allocate supplemental channels is made when the remainingtraffic resources fall below y. The de-allocation request is triggeredonly during a resource allocation by the CRM 44.

In the event of a soft handoff request for a fundamental channel, theCRM 44 maintains information specifying whether or not a particular TCEis handling a fundamental or a supplemental code channel.

In general, supplemental channels are de-allocated before an associatedfundamental channel is de-allocated. If the SBS 54 does not de-allocatesupplemental channels before fundamental channels, the base station 18can de-allocate the supplemental channels or wait for a danglingresource to de-allocate the channels.

For a soft handoff, the CRM 44 allocates supplemental channels requestedin a CRMRLM resource request message, i.e., a CRMRLM_ResourceRelReqmessage.

For a softer handoff, the CRM 44 places allocated channel elements insofter handoff. Additional supplemental channel elements are notallocated for a softer handoff.

FIG. 3 is a ping-pong diagram illustrating messages exchanged betweenthe RLM 58, CRM 44, and the TCE 48 of FIG. 2 to set up a call inaccordance with the teachings of the present invention. To assignsupplemental channels to a call, the RLM 58 sends a CRMRLM_ResourceReqmessage to the CRM 44 requesting a release of n supplementary channels.In response to the CRMRLM_ResourceReq message, the CRM 44 sends aCRMTCE_AllocateCmd message to the TCE 48 commanding the TCE 48 torelease a supplemental channel. The TCE 48 responds with aCRMTCE_AllocateRsp message indicating that the supplementary channel wasreleased. n CRMTCE_AllocateCmd messages and n CRMTCE_AllocateRspmessages are exchanged between the CRM 44 and the TCE 48, one for eachsupplementary channel released.

After the message exchange between the CRM 44 and the TCE 48, the CRM 44sends a CRMRLM_ResourceRelRsp message to the RLM 58 informing the RLM 58that n supplementary channels were allocated.

With access to the present teachings, those skilled in the art caneasily construct the messages of FIG. 3. The following discussion ofchanges required to IS-95 to accommodate messages exchanged between theRLM 58 and the CRM 44 is intended to facilitate an understanding of thepresent invention.

For the CRMRLM_CRMResourceReq message, changes are required to allow theRLM 58 to request multiple resources from the TCE 48 in one resourcerequest message. A CRMResourceReqType field is still used to specify whythe resources are needed (e.g. handoff, origination, etc.). For example,if resources for one fundamental channels, termed fundamentals, and 5forward supplementary channels, termed supplementals, are requested forhandoff, the CRMResourceReqType field is set to _HANDOFF, theFundamentalIncluded field is set to TRUE, and theNumFwdSupChannelsRequested is set to 5.

Alternatively, if resources for 3 forward supplementals are requested bythe RLM 58 to increase the data throughput of a medium data rate (MDR)call, the CRMResourceReqType field is set to _ORIGINATION, theFundamentalIncluded field is set to FALSE, and theNumFwdSupChannelsRequested is set to 3.

The field FundamentalFwdTrafficGain is used by the CRM 44 to predict theforward power requirements of requested supplemental channels of type_ORIGINATION for admission control purposes. The fields ForwardRateSetand ReverseRateSet have been added to support IS-95C.

Table 1 illustrates changes to the CRMRLM_CRMResourceReq networkoperation interface specification (NOIS) message.

TABLE 1 Parameter Type Comments/description CallId M A unique 64-bit tagassociated with a call event. This tag follows the call and is used tomark resources that are allocated to it in the various subsystems. Itincludes: SID, EntryPoint, Count, Time. IMSI O TransactionId M Indicatesthe transaction identifier for the current request-response pair and isused to correlate the response with the request. It is incremented everytime a request is made for a given CallId. CRMResourceRequest MEnumeration: _ORIGINATION or Type _HANDOFF. CellId O Mandatory ifExtendedBaseId is omitted. It includes: CellNumber, SectorId. Alwayspresent in S/W Rel. 3.5. ExtendedBaseId O Mandatory if CellId isomitted. It includes: BAND_CLASS, CDMA_FREQ, CellNumber, SectorId. Neverused in S/W Rel. 3.5. FRAME_OFFSET O Mandatory when the request type isHANDOFF and must be the same for all TCES 48 carrying involved in thesame call. It must be omitted otherwise. EnableTA O Set equal to 1 onlywhen the temporal analyzer is enabled for this call. CallLogging O Setequal to 1 only when diagnostic logging is enabled for this call.FundamentalIncluded M Explicit Boolean. Enumeration: TRUE: Fundamentalrequested FALSE: Fundamental not requested NumFwdSupChannels O Integerof ACLRL_NumSupChannelType ACLRL_MaxNumSupChannels = 0x07NumRvsSupChannels O Integer of ACLRL_NumSupChannelTypeACLRL_MaxNumSupChannels = 0x07 FundamentalFwd O included in forwardsupplemental TrafficGain originations only: the full-rate forward linktraffic channel gain of the fundamental associated with the supplementalcode channel requested. ForwardRateSet O Forward Rate Set, ranges from 1to 6. ReverseRateSet O Reverse Rate Set, ranges from 1 to 6.

The CRMRLM_CRMResourceRsp Message has been extended to allow anycombination of fundamental, forward supplemental or reverse supplementalchannels to be granted in the same message. The existing fields of themessage are used to allocate the fundamental, and five new fields areadded to specify the forward and reverse supplementals.

Table 2 illustrates required changes to the CRMRLM_ResourceRsp NOISmessage.

TABLE 2 Parameter Type Comments/description CallId M A unique 64-bit tagassociated with a call event. This tag follows the call and is used tomark resources that are allocated to it in the various subsystems. Itincludes: SID, EntryPoint, Count, Time. TransactionId M It must matchthe TransactionId used for the corresponding resource request.CRMResource M Enumeration: RESRC_ALLOCATED, RequestStatusRESRC_NOT_ALLOCATED, CRM_NOT_READY (not used), REJECT_BAD_BASE_ID,CSM_REJECT ExtendedBaseId O Always used. In the case of the 6-sectorBTS, with 2*3 frequency/sectors configuration, its CellId portion can beset differently from what received in the resource request; this happensin case CEs are not available in the cluster associated with thefrequency requested by the RLM 58, and to route the call setup to theother frequency where resources are available. SectorList O Used whenthe corresponding resource request type is HANDOFF and the CRM 44establishes that it is a softer handoff. It lists the ExtendedBaseId'sof all sectors in softer handoff for this CallId. Omitted if it is ofthe type ORIGINATION. ACNNodeId O Omitted if the resource request typeis HANDOFF and SectorList count is ≦3 (maximum number of links in softerhandoff that can be supported by the CSM). Mandatory otherwise.CODE_CHAN O Mandatory when the request status is ALLOCATED. FRAME_OFFSETO Mandatory when the request type is ORIGINATION. Omitted if it is ofthe type HANDOFF. TCERLMLinkVersion O Although optional, it is alwaysincluded. Fundamental M Enumeration: Included TRUE: Fundamentalallocated FALSE: Fundamental not allocated FwdSupChannelList M IncludesNumFwdSupChannels and a list of Code Channels and ACNNodeIdRvsSupChannelList O Includes NumRvsSupChannels and a list of ACNNodeIdFwdSupChannelList NumFwdSupChannels O Integer of ACLRL_NumSupChannelTypeACLRL_MaxNumSupChannels = 0x07 CODE_CHAN O This parameter must berepeated exactly NumFwdSupChannels times ACNNodeId O This parameter mustbe repeated exactly NumFwdSupChannels times RvsSupChannelListNumRvsSupChannels O Integer of ACLRL_NumSupChannelTypeACLRL_MaxNumSupChannels = 0x07 ACNNodeId O This parameter must berepeated exactly NumFwdSupChannels times

The CRMRLM_CRMResourceReleaseReq Message has also been generalized toallow the release of any combination of fundamental, forwardsupplemental and/or reverse supplementals. If a forward supplementalchannel is released, the inclusion of the fundamental forward gainallows the CRM 44 to estimate how much forward power might becomeavailable for other users in that sector.

Table 3 illustrates changes required to the RMRLM_CRMResourceReleaseReqNOIS message.

TABLE 3 Parameter Type Comments/description CallId M A unique 64-bit tagassociated with a call event. This tag follows the call and is used tomark resources that are allocated to it in the various subsystems. Itincludes: SID, EntryPoint, Count, Time. TransactionId M It indicates thetransaction identifier for the current request-response pair and is usedto correlate the response with the request. It is incremented every timea request is made for a given CallId. ExtendedBaseId M TCELinkStatus MEnumeration: VALID, NOT_VALID. Fundamental M Enumeration: Included TRUE:Fundamental should also be released. FALSE: Fundamental should not bereleased. FwdSupChannels O It includes NumFwdSupChannels and a list ofACNNodeId RvsSupChannels O It includes NumRvsSupChannels and a list ofACNNodeId FwdSupChannels NumFwdSupChannels O Integer ofACLRL_NumSupChannelType ACLRL_MaxNumSupChannels = 0x07 ACNNodeId O Thisparameter must be repeated exactly NumFwdSupChannels timesRvsSupChannels NumRvsSupChannels O Integer of ACLRL_NumSupChannelTypeACLRL_MaxNumSupChannels = 0x07 ACNNodeId O This parameter must berepeated exactly NumFwdSupChannels times

FIG. 4 is a ping-pong diagram illustrating messages exchanged betweenthe RLM 58 the CRM 44, and the TCE 48 of FIG. 2 to facilitate mobilestation handoff between a requester communications system (not shown)that includes a requestor BSC (not shown) having a requestor RLM (RLM2)70.

Initially, the requestor RLM 70 transfers a CRMRLM_ResourceReq message,i.e., a handoff message to the CRM 44. Conventionally, if the CRM 44 didnot have sufficient resources to accept the handoff, the call beinghanded off would be dropped, i.e., blocked at the CRM 44. In the presentspecific embodiment detailed in FIG. 4, if the CRM 44 determines thatinsufficient traffic resources such as fundamental channels areavailable to accept the handoff, a CRMRLM_SuppRelReq to release msupplementary channels is sent to the RLM 58. The RLM 58 subsequentlysends a CRMTCE_ResourceRelReq message to the CRM 44 directing the CRM 44to release m supplementary channels from the TCE 48. The CRM 44acknowledges the receipt of the message in a CRMTCE_ResourceRelRsp tothe RLM 58 and subsequently sends a CRMTCE_DeallocateReq message to theTCE 48 requesting that the TCE 48 de-allocate a supplementary channel sothat it may be used for traffic channels. The TCE 48 responds with aCRMTCE_DeallocateRsp indicating that a supplemental channel wasde-allocated. The CRM 44 and the TCE 48 exchange m CRMTCE_DeallocateReqmessages and m CRMTCE_DeallocateRsp messages, one for each msupplemental that is de-allocated. After the m supplemental channels arede-allocated, the CRM 44 sends a CRMRLM_ResourceReqRsp response messageback to the requester RLM 70 indicating that the handoff can now becompleted.

With access to the present teachings, those skilled in the art canconstruct the messages of FIG. 4.

FIG. 5 is a flow diagram of a method 80 for strategically allocatingsupplemental channels to reduce dropped calls during handoff implementedwithin the base station controller 54 of FIG. 2. The method 80 isimplemented by software running on the computer 46 of FIG. 2.

With reference to FIGS. 2 and 5, in an initial monitoring step 82, theCRM 44 is monitored for blocked handoff or call origination requestsfrom a source BSC (not shown). If the CRM 82 does not block the callassociated with the handoff request, the method 80 is complete. If theCRM 44 blocks the call, control is passed to an estimation step 84,where the time required to de-allocate supplemental resources andreallocate them as traffic resources is estimated in accordance withprocedures known in the art. If the time required is less than apredetermined amount, control is passed to a resource management step86. The predetermined amount of time is application-specific and roughlycorresponds to the time after which the call is likely to be dropped dueto a time-out condition.

In the resource management step 86, the number of supplemental channelscurrently in use or otherwise available for reallocation as trafficchannels at the target BSC 14 is checked. The software subsequentlycauses the target BSC 14 to generate a supplemental channel releaserequest.

In a subsequent resource releasing step 88, supplemental channels arereleased in accordance with the supplemental channel release request bythe target BSC 14. Newly available supplemental resources may then bereallocated as needed by the BTS CRM 44 as traffic resources tofacilitate handoff or call origination.

In summary, the method 80 involves checking the supplemental channelscurrently in use or otherwise available for reallocation as trafficchannels at a target BSC; requesting the target BSC to issue asupplemental channel release request, upon completion of which theassociated target BTS CRM can reallocate the available supplementalresources as traffic resources that are sufficient to accommodate thehandoff or origination as requested by the source BSC.

FIG. 6 is a flow diagram of a method 90 for allocating supplementalchannels and traffic channels according to the present invention. Withreference to FIGS. 2 and 6, initially, in a threshold-establishing step92, a threshold is established for traffic resources. Control is thenpassed to a traffic resource-checking step 94 where currently availabletraffic resources are monitored. If currently available trafficresources are greater than the threshold, then the method 90 iscomplete. If available traffic resources drop below the threshold,control is passed to a resource allocation step 96, where a request isinitiated from the target BTS CRM 44 to the BSC SBS 54 requesting thatthe BSC SBS 54 issue a supplemental channel release request to thetarget BTS 18.

Control is subsequently passed to a supplemental resource releasing step98, where supplemental resources at the BTS 18 are de-allocated inaccordance with the supplemental channel release request from the BSCSBS 54. Newly available channel elements associated with the releasedsupplemental channels are converted to traffic channel elements untilthe current traffic resources are greater than the predeterminedthreshold.

In summary, the method 90 involves initiating a request from a targetBTS CRM to an associated BSC SBS requesting that the BSC SBS issue asupplemental channel release request to the BTS, upon completion ofwhich the target BTS can reassign channel elements associated with thesupplemental channels to traffic channel elements until the currenttraffic resources are greater than a predetermined threshold.

Thus, the present invention has been described herein with reference toa particular embodiment for a particular application. Those havingordinary skill in the art and access to the present teachings willrecognize additional modifications, applications, and embodiments withinthe scope thereof.

It is therefore intended by the appended claims to cover any and allsuch applications, modifications and embodiments within the scope of thepresent invention.

Accordingly,

What is claimed is:
 1. A system for reducing dropped calls in a wirelesscommunications network comprising: means for determining currentlyavailable wireless communications system traffic resources; means forestimating that a time required for a request for release ofsupplemental resources to be sent, a response to be sent back, forsupplemental resources to be de-allocated and reallocated as trafficchannels will not cause a dropped call; means for transmitting saidrequest for release of supplemental resources in response to determiningcurrently available wireless communications system traffic resources;and means for selectively de-allocating wireless communications systemsupplemental resources and providing said supplemental resources for useas traffic resources in response to said request for release ofsupplement resources.
 2. The system of claim 1 wherein said currentlyavailable wireless communications system traffic resources includecurrently available traffic channels.
 3. The system of claim 1 whereinsaid wireless communications system supplemental resources includesupplemental channels.
 4. The system of claim 1 wherein said means fordetermining includes means for comparing a number of used trafficchannels with a number of total traffic channels and providing saidrequest when the difference between said number of total trafficchannels and said number of used traffic channels is less than athreshold.
 5. The system of claim 1 wherein said means for determiningincludes means for monitoring when a call handoff request and/or a callorigination request is blocked at a base station transceiver subsystemcall resource manager and providing said request when said call isblocked.
 6. The system of claim 5 wherein said means for selectivelyde-allocating includes means for sending a message to a selector banksubsystem radio link manager, receiving a first response from saidselector bank subsystem radio link manager, requesting a de-allocationof said supplemental resources, and upon completion of de-allocation inresponse to said de-allocation request, reallocating said supplementalresources as traffic resources by controlling corresponding trafficchannel elements.
 7. The system of claim 6 further including means forestimating said time required by said means for sending said request,receiving said response, de-allocating said supplemental resources, andreallocating said supplemental resources, and disabling said means forsending said request if said time is larger than a predetermined time.8. The system of claim 6 wherein said means for selectivelyde-allocating includes software running on a base station transceiversubsystem.
 9. The system as in claim 1, further comprising: means forselectively de-allocating wireless communications system supplementalresources and providing said supplemental resources for use as trafficresources as a function of the currently in-use supplemental resourcesand the estimated time.
 10. The system as in claim 1, furthercomprising: means for determining currently in-use supplementalresources.
 11. The system as in claim 10, wherein said means forselectively de-allocating wireless communications system supplementalresources further comprises: means for selectively de-allocatingwireless communications system fundamental resources and providing saidfundamental resources for use as traffic resources.
 12. The system as inclaim 1, further comprising: means for determining currently in-usesupplemental resources, wherein said means for selectively de-allocatingwireless communications system supplemental resources and providing saidsupplemental resources for use as traffic resources further comprises:means for selectively de-allocating wireless communications systemsupplemental resources and providing said supplemental resources for useas traffic resources as a function of the currently in-use supplementalresources.
 13. A system for managing traffic resources and supplementaryresources in a wireless communications system comprising: means formaintaining a predetermined threshold for traffic resources; means fordetermining if currently available traffic resources are below saidthreshold and providing a request for release of supplemental resourcesin response thereto; means for estimating that a time required for saidrequest for release of supplemental resources to be sent, a response tobe sent back, for supplemental resources to be de-allocated andreallocated as traffic channels will not cause a dropped call; and meansfor de-allocating in-use supplementary resources and reallocating saidsupplementary resources as traffic resources so that said trafficresources are above said threshold in response to said request.
 14. Thesystem of claim 13 wherein said means for de-allocating includes meansfor initiating a request from a call resource manager in a base stationtransceiver subsystem to a selector bank subsystem within a base stationcontroller governing said wireless communications system to reassignchannel elements associated with supplemental channels to trafficchannel elements.
 15. A method for reducing dropped calls in a wirelesscommunications network comprising the steps of: determining currentlyavailable wireless communications system traffic resources and providinga request for release of supplemental resources in response thereto;estimating a time required for a request for release of supplementalresources to be sent, a response to be sent back, for supplementalresources to be de-allocated and reallocated as traffic channels; andselectively de-allocating wireless communications system supplementalresources and reallocating said supplemental resources as trafficresources in response to said request.
 16. The method of claim 15,wherein said currently available wireless communications system trafficresources include currently available traffic channels.
 17. The methodof claim 15, wherein said wireless communications system supplementalresources include supplemental channels.
 18. The method of claim 15,wherein said determining includes comparing a number of used trafficchannels with a number of total traffic channels and providing saidrequest when the difference between said number of total trafficchannels and said number of used traffic channels is less than athreshold.
 19. The method of claim 15, wherein said determining includesmonitoring when a call handoff request and/or a call origination requestis blocked at a base station transceiver subsystem call resource managerand providing said signal when said call is blocked.
 20. The method ofclaim 15, where said selectively de-allocating includes sending amessage to a selector bank subsystem radio link manager, requesting ade-allocation in response to said de-allocation request, reallocatingsaid supplemental resources as traffic resources by controllingcorresponding traffic channel elements.
 21. The method of claim 20further comprising disabling said sending a message if said estimatedtime is larger than a predetermined time.
 22. A method for managingtraffic resources and supplementary resources in a wirelesscommunications system, comprising: maintaining a threshold for trafficresources; determining if currently available traffic resources arebelow said threshold and providing a signal in response thereto;estimating a time required for a request for release of in-usesupplemental resources to be sent, a response to be sent back, forin-use supplemental resources to be de-allocated and reallocated astraffic channels; and de-allocating in-use supplementary resources andreallocating said supplementary resources as traffic resources so thatsaid traffic resources are above said threshold in response to saidsignal.
 23. The method of claim 22, wherein said de-allocating includesinitiating a request from a call resource manager in a base stationtransceiver subsystem to a selector bank subsystem within a base stationcontroller governing said wireless communication system to reassignchannel elements associated with supplemental channels to trafficchannel elements.
 24. A base station, comprising: a call resourcemanager that receives a request for release of a supplemental channel,receives a time estimate for a request for release of the supplementalchannel to be sent, a response to be sent back, for the supplementalchannel to be de-allocated and reallocated as a traffic channel; and ifthe time estimate is above a predetermined value, commands a release ofthe supplemental channel, receives a response indicating release of thesupplemental channel, and sends a response message indicating allocationof the released supplemental channel.
 25. The base station of claim 24further comprising an overhead channel manager that manages access andregistration messages.
 26. A base station, comprising: a call resourcemanager that receives a handoff message from a first mobile station,receives a time estimate for a request for release of supplementalchannels to be sent, a response to be sent back, for the supplementalchannels to be de-allocated and reallocated as traffic channels; sends afirst release m supplemental channels (m≧1) message to a second mobilestation, receives a second release m supplemental channels message fromthe second mobile station, sends to the second mobile station, aresponse message to the second release m supplemental channels message,sends a de-allocate request message requesting de-allocation of a msupplemental channels, receives a de-allocate response message for everysupplemental channel indicating a supplemental channel was de-allocated,and sends a resource response message to the first mobile stationindicating the m supplemental channels were de-allocated; and a trafficchannel element that allocates and releases the m supplemental channels.